u ANALOG DEVICES
REV. A
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AD22151
Linear Output
Magnetic Field Sensor
FEATURES
Adjustable Offset to Unipolar or Bipolar Operation
Low Offset Drift over Temperature Range
Gain Adjustable over Wide Range
Low Gain Drift over Temperature Range
Adjustable First Order Temperature Compensation
Ratiometric to VCC
APPLICATIONS
Automotive
Throttle Position Sensing
Pedal Position Sensing
Suspension Position Sensing
Valve Position Sensing
Industrial
Absolute Position Sensing
Proximity Sensing
FUNCTIONAL BLOCK DIAGRAM
TEMP REF
I
SOURCE
DEMODSWITCHES
OUT AMP
REF
V
CC
/2
AD22151
GENERAL DESCRIPTION
The AD22151 is a linear magnetic field transducer. The sensor
output is a voltage proportional to a magnetic field applied
perpendicularly to the package top surface.
The sensor combines integrated bulk Hall cell technology and
instrumentation circuitry to minimize temperature related drifts
associated with silicon Hall cell characteristics. The architecture
maximizes the advantages of a monolithic implementation while
allowing sufficient versatility to meet varied application require-
ments with a minimum number of components.
Principal features include dynamic offset drift cancellation
and a built-in temperature sensor. Designed for single 5 V
supply operation, the AD22151 achieves low drift offset and
gain operation over –40C to +150C. Temperature compensa-
tion can accommodate a number of magnetic materials commonly
utilized in economic position sensor assemblies.
The transducer can be configured for specific signal gains to
meet various application requirements. Output voltage can be
adjusted from fully bipolar (reversible) field operation to fully
unipolar field sensing.
The voltage output achieves near rail-to-rail dynamic range,
capable of supplying 1 mA into large capacitive loads. The
signal is ratiometric to the positive supply rail in all configurations.
NC
R1
GND
R3
R2
V
CC
AD22151
NC = NO CONNECT
OUTPUT
0.1F
Figure 1. Typical Bipolar Configuration with Low
(< –500 ppm) Compensation
NC
R1
GND
R3
R2
V
CC
AD22151
NC = NO CONNECT
OUTPUT
0.1F
R4
Figure 2. Typical Unipolar Configuration with
High (
–2000 ppm) Compensation
WARNING!
REV. A–2–
AD22151–SPECIFICATIONS
(TA = 25C and V+ = 5 V, unless otherwise noted.)
Parameter Min Typ Max Unit
OPERATION
V
CC
Operating 4.5 5.0 6.0 V
I
CC
Operating 6.0 10 mA
INPUT
TC3 (Pin 3) Sensitivity/Volt 160 mV/G/V
Input Range
1
VCC
205±.
V
OUTPUT
2
Sensitivity (External Adjustment, Gain = +1) 0.4 mV/G
Linear Output Range 10 90 % of V
CC
Output Min 5.0 % of V
CC
Output Max (Clamp) 93 % of V
CC
Drive Capability 1.0 mA
Offset @ 0 Gauss
VCC
2
V
Offset Adjust Range 5.0 95 % of V
CC
Output Short Circuit Current 5.0 mA
ACCURACIES
Nonlinearity (10% to 90% Range) 0.1 % FS
Gain Error (Over Temperature Range) ±1%
Offset Error (Over Temperature Range) ±6.0 G
Uncompensated Gain TC (G
TCU
)950 ppm
RATIOMETRICITY ERROR 1.0 %V/V
CC
3 dB ROLL-OFF (5 mV/G) 5.7 kHz
OUTPUT NOISE FIGURE (6 kHz BW) 2.4 mV/rms
PACKAGE 8-Lead SOIC
OPERATING TEMPERATURE RANGE –40 +150 C
NOTES
1
–40C to +150C.
2
R
L
= 4.7 kW.
Specifications subject to change without notice.
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although the
AD22151 features proprietary ESD protection circuitry, permanent damage may occur on devices
subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended
to avoid performance degradation or loss of functionality.
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 V
Package Power Dissipation . . . . . . . . . . . . . . . . . . . . . . 25 mW
Storage Temperature . . . . . . . . . . . . . . . . . . . –50C to +160C
Output Sink Current, I
O
. . . . . . . . . . . . . . . . . . . . . . . . 15 mA
Magnetic Flux Density . . . . . . . . . . . . . . . . . . . . . . Unlimited
Lead Temperature (Soldering 10 sec) . . . . . . . . . . . . . . 300C
*Stresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those indicated in the operational
sections of this specification is not implied. Exposure to the absolute maximum
rating conditions for extended periods may affect device reliability.
ORDERING GUIDE
Temperature Package Package
Model Range Description Option
AD22151YR –40C to +150C8-Lead SOIC R-8
AD22151YR-REEL –40C to +150C8-Lead SOIC R-8
3333 3333 _|:|:|:L AREA or _|:|:|:L
REV. A
AD22151
–3–
PIN CONFIGURATION
TOP VIEW
(Not to Scale)
8
7
6
5
1
2
3
4
AREA OF SENSITIVITY*
TC1
TC2
TC3
GND
V
CC
REF
GAIN
OUTPUT
AD22151
(Not to Scale)
8
7
6
5
1
2
3
4
*SHADED AREA REPRESENTS
MAGNETIC FIELD AREA OF
SENSITIVITY (20MILS 20MILS)
POSITIVE B FIELD INTO TOP OF
PACKAGE RESULTS IN A POSITIVE
VOLTAGE RESPONSE
CIRCUIT OPERATION
The AD22151 consists of epi Hall plate structures located at the
center of the die. The Hall plates are orthogonally sampled by
commutation switches via a differential amplifier. The two
amplified Hall signals are synchronously demodulated to provide a
resultant offset cancellation (see Figure 3). The demodulated
signal passes through a noninverting amplifier to provide final
gain and drive capability. The frequency at which the output
signal is refreshed is 50 kHz.
TEMPERATURE –
C
140 –40120 100 80 60 40 20 0 –20
–0.004
OFFSET – V
–0.003
–0.002
–0.001
0
0.001
0.002
0.003
0.004
0.005
Figure 3. Relative Quiescent Offset vs. Temperature
TEMPERATURE DEPENDENCIES
The uncompensated gain temperature coefficient (G
TCU
) of the
AD22151 is the result of fundamental physical properties asso-
ciated with silicon bulk Hall plate structures. Low doped Hall
plates operated in current bias mode exhibit a temperature
relationship determined by the action of scattering mechanisms
and doping concentration.
The relative value of sensitivity to magnetic field can be altered
by the application of mechanical force upon silicon. The mecha-
nism is principally the redistribution of electrons throughout the
PIN FUNCTION DESCRIPTIONS
Pin No. Description Connection
1Temperature Compensation 1 Output
2Temperature Compensation 2 Output
3Temperature Compensation 3 Input/Output
4Ground
5Output Output
6Gain Input
7Reference Output
8Positive Power Supply
“valleys” of the silicon crystal. Mechanical force on the sensor is
attributable to package-induced stress. The package material
acts to distort the encapsulated silicon, altering the Hall cell
gain by ±2% and G
TCU
by ±200 ppm.
Figure 4 shows the typical G
TCU
characteristic of the AD22151.
This is the observable alteration of gain with respect to tempera-
ture with Pin 3 (TC3) held at a constant 2.5 V (uncompensated).
If a permanent magnet source used in conjunction with the
sensor also displays an intrinsic TC (B
TC
), it will require factoring
into the total temperature compensation of the sensor assembly.
Figures 5 and 6 represent typical overall temperature/gain per-
formance for a sensor and field combination (B
TC
= –200 ppm).
Figure 5 is the total drift in volts over a –40C to +150C tem-
perature range with respect to applied field. Figure 6 represents
typical percentage gain variation from 25C. Figures 7 and 8
show similar data for a B
TC
= –2000 ppm.
TEMPERATURE – C
14
–4
–40
% GAIN
10 60 110 160
12
4
2
0
–2
10
6
8
–6
Figure 4. Uncompensated Gain Variation (from
25
C) vs. Temperature
REV. A–4–
AD22151
FIELD – Gauss
–600 400–400 –200 0 200
0
DELTA SIGNAL – V
0.005
0.010
0.015
0.020
0.025
600
Figure 5. Signal Drift over Temperature (–40
C to
+150
C) vs. Field (–200 ppm); 5 V Supply
TEMPERATURE – C
0.25
% GAIN
0.20
0
0.15
0.05
0.10
–40 10 60 110 160
–0.05
Figure 6. Gain Variation from 25
C vs. Temperature
(–200 ppm) Field; R1 –15 k
W
FIELD – Gauss
–600 400
–400 –200 0 200
DELTA SIGNAL – V
0
0.010
0.015
0.020
0.025
600
0.005
0.045
0.040
0.030
0.035
–800 800
Figure 7. Signal Drift over Temperature (–40
C to
+150
C) vs. Field (–2000 ppm); 5 V Supply
TEMPERATURE – C
2.0
1.8
1.0
1.6
1.2
1.4
–40 10 60 110 160
–0.2
0.8
0.6
0.4
0.2
0
% GAIN
Figure 8. Gain Variation (from 25
C) vs. Temperature
(–2000 ppm Field; R1 = 12 k
W
)
TEMPERATURE COMPENSATION
The AD22151 incorporates a “thermistor” transducer that
detects relative chip temperature within the package. This
function provides a compensation mechanism for the various
temperature dependencies of the Hall cell and magnet combina-
tions. The temperature information is accessible at Pins 1 and
2 ( +2900 ppm/C) and Pin 3 ( –2900 ppm/C), as repre-
sented by Figure 9. The compensation voltages are trimmed
to converge at V
CC
/2 at 25C. Pin 3 is internally connected to
the negative TC voltage via an internal resistor (see the Func-
tional Block Diagram). An external resistor connected between
Pin 3 and Pins 1 or 2 will produce a potential division of the
two complementary TC voltages to provide optimal compensa-
tion. The Pin 3 internal resistor provides a secondary TC
designed to reduce second order Hall cell temperature sensitivity.
TEMPERATURE – C
1.0
VOLTS – Reference
0.8
0
0.6
0.2
0.4
150 112 74 –2 –40
–0.2
–0.4
–0.6
–0.8
–1.0
36
TC1, TC2 VOLTS
TC3 VOLTS
Figure 9. TC1, TC2, and TC3 with Respect to Reference
vs. Temperature
The voltages present at Pins 1, 2, and 3 are proportional to the
supply voltage. The presence of the Pin 2 internal resistor dis-
tinguishes the effective compensation ranges of Pins 1 and 2.
(See temperature configuration in Figures 1 and 2, and typical
resistor values in Figures 10 and 11.)
Variation occurs in the operation of the gain temperature com-
pensation for two reasons. First, the die temperature within the
package is somewhat higher than the ambient temperature due
m 7 m
REV. A
AD22151
–5–
to self-heating as a function of power dissipation. Second, pack-
age stress effect alters the specific operating parameters of the
gain compensation, particularly the specific crossover tempera-
ture of TC1, TC3 ( ±10C).
CONFIGURATION AND COMPONENT SELECTION
There are three areas of sensor operation that require external
component selection: temperature compensation (R1), signal
gain (R2 and R3), and offset (R4).
Temperature
If the internal gain compensation is used, an external resistor is
required to complete the gain TC circuit at Pin 3. A number of
factors contribute to the value of this resistor:
a. The intrinsic Hall cell sensitivity TC 950 ppm.
b. Package induced stress variation in a. ±150 ppm.
c. Specific field TC –200 ppm (Alnico), –2000 ppm
(Ferrite), 0 ppm (electromagnet), and so on.
d. R1, TC.
The final value of target compensation also dictates the use of
either Pin 1 or Pin 2. Pin 1 is provided to allow for large nega-
tive field TC devices such as ferrite magnets; thus, R1 would be
connected to Pins 1 and 3.
Pin 2 uses an internal resistive TC to optimize smaller field
coefficients such as Alnico down to 0 ppm coefficients when
only the sensor gain TC itself is dominant. Because the TC of
R1 itself will also affect the compensation, a low TC resistor
(±50 ppm) is recommended.
Figures 10 and 11 indicate R1 resistor values and their associ-
ated effectiveness for Pins 1 and 2, respectively. Note that the
indicated drift response in both cases incorporates the intrinsic
Hall sensitivity TC (B
TCU
).
For example, the AD22151 sensor is to be used in conjunction
with an Alnico material permanent magnet. The TC of such mag-
nets is –200 ppm (see Figures 5 and 6). Figure 11 indicates
that a compensating drift of 200 ppm at Pin 3 requires a nomi-
nal value of R1 = 18 kW (assuming negligible drift of R1 itself).
R1 – k
3500
DRIFT – ppm
3000
1000
2500
1500
2000
0510 20 25
500
0
15 30
Figure 10. Drift Compensation (Pins 1 and 3) vs.
Typical Resistor Value R1
R1 – k
800
DRIFT – ppm
600
–200
400
0
200
0510 20 25
–400
–600
15 30 35 40 45 50
Figure 11. Drift Compensation (Pins 2 and 3) vs.
Typical Resistor Value R1
GAIN AND OFFSET
The operation of the AD22151 can be bipolar (i.e., 0 Gauss =
V
CC
/2), or a ratiometric offset can be implemented to position
Zero Gauss point at some other potential (i.e., 0.25 V).
The gain of the sensor can be set by the appropriate R2 and R3
resistor values (see Figure 1) such that:
Gin R
RmV Ga =+ ¥13
204./
(1)
However, if an offset is required to position the quiescent out-
put at some other voltage, the gain relationship is modified to:
Gin R
RR mV Ga =+
()
¥13
24 04./
(2)
The offset that R4 introduces is:
Offset R
RR VV
CC OUT
=+ +
()
¥
()
13
24
(3)
For example, at V
CC
= 5 V at room temperature, the internal gain of
the sensor is approximately 0.4 mV/Gauss. If a sensitivity of
6 mV/Gauss is required with a quiescent output voltage of 1 V,
the calculations below apply (see Figure 2).
A value would be selected for R3 that complied with the various
considerations of current and power dissipation, trim ranges (if
applicable), and so on. For the purpose of example, assume a
value of 85 kW.
To achieve a quiescent offset of 1 V requires a value for R4 as:
V
V
CC
CC
21
0 375
Ê
Ë
Áˆ
¯
˜
=
.
(4)
Thus:
Rkkk485
0 375 85 141 666=Ê
Ë
Áˆ
¯
˜=
WWW
.–.
(5)
The gain required would be 6/0.4 (mV/Gauss) = 15.
\\ \\ - l—I El: - m Bw PSD «am/muss»
REV. A–6–
AD22151
Knowing the values of R3 and R4 and noting Equation 2, the
parallel combination of R2 and R4 required is:
85
15 1 6 071
kk
.
()
=
Thus:
R
kk
k21
1
6 071
1
141 666
6 342=
=
..
.
ΩΩ
NOISE
The principal noise component in the sensor is thermal noise
from the Hall cell. Clock feedthrough into the output signal is
largely suppressed with application of a supply bypass capacitor.
Figure 12 shows the power spectral density (PSD) of the output
signal for a gain of 5 mV/Gauss. The effective bandwidth of the
sensor is approximately 5.7 kHz, as shown in Figure 13. The
PSD indicates an rms noise voltage of 2.8 mV within the 3 dB
bandwidth of the sensor. A wideband measurement of 250 MHz
indicates 3.2 mV rms (see Figure 14a).
In many position sensing applications, bandwidth requirements
can be as low as 100 Hz. Passing the output signal through a
100 Hz LP filter, for example, would reduce the rms noise volt-
age to 1 mV. A dominant pole may be introduced into the
output amplifier response by connection of a capacitor across
feedback resistor R3 as a simple means of reducing noise at the
expense of bandwidth. Figure 14b indicates the output signal of
a 5 mV/G sensor bandwidth limited to 180 Hz with a 0.01 µF
feedback capacitor.
Note: Measurements were taken with a 0.1 µF decoupling
capacitor between V
CC
and GND at 25°C.
LOGMAG
5 dB/div
100H
1H
START: 64Hz
NOISE: PSD
(
8mV/GAUSS
)
STOP: 25.6kHz
RMS: 64
B MARKER 64Hz Y: 3.351H
Figure 12. Power Spectral Density (5 mV/G)
GAIN – mV/Gauss
23456
FREQUENCY – kHz
0
2
3
4
5
1
6
7
1
3dB FREQUENCY (kHz)
Figure 13. Small Signal Gain Bandwidth vs. Gain
CH2 10.0mV
BW
M2.00ms
[
[T
3ACQS
CH2 p-p
19.2mV
TEK STOP: 25.0 kS/s
Figure 14a. Peak-to-Peak Full Bandwidth (10 mV/Division)
BW
M2.00ms
[
[T
7ACQS
CH2 p-p
4.4mV
TEK STOP: 25.0 kS/s
CH2 10.0mV
Figure 14b. Peak-to-Peak 180 Hz Bandwidth
(10 mV/Division)
REV. A
AD22151
–7–
OUTLINE DIMENSIONS
8-Lead Standard Small Outline Package [SOIC]
Narrow Body
(R-8)
Dimensions shown in millimeters and (inches)
0.25 (0.0098)
0.19 (0.0075)
1.27 (0.0500)
0.41 (0.0160)
0.50 (0.0196)
0.25 (0.0099) 45
8
0
1.75 (0.0688)
1.35 (0.0532)
SEATING
PLANE
0.25 (0.0098)
0.10 (0.0040)
85
41
5.00 (0.1968)
4.80 (0.1890)
4.00 (0.1574)
3.80 (0.1497)
1.27 (0.0500)
BSC
6.20 (0.2440)
5.80 (0.2284)
0.51 (0.0201)
0.33 (0.0130)
COPLANARITY
0.10
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
COMPLIANT TO JEDEC STANDARDS MS-012AA
FIELD – Gauss
0.06
0.05
0.04
0.02
0.03
–600 –400 –200 0 200 400 600
0.01
0
–0.01
–0.02
–0.03
–0.04
–0.05
% ERROR
Figure 15. Integral Nonlinearity vs. Field
TEMPERATURE – C
2.496
VOLTS
2.494
2.492
2.488
2.490
140 120 100 80 60 40 20
2.486
2.484
0–40–20
GAIN = 3.78mV/G
Figure 16. Absolute Offset Volts vs. Temperature
REV. A
C00675–0–2/03(A)
PRINTED IN U.S.A.
–8–
AD22151
Revision History
Location Page
2/03—Data Sheet changed from REV. 0 to REV. A.
Change to ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7